MINOR: peers/cli: do not dump the peers dictionaries by default on "show peers"

MINOR: peers/cli: do not dump the peers dictionaries by default on "show peers"

The "show peers" output has become huge due to the dictionaries making it
less readable. Now this feature has reached a certain level of maturity
which doesn't warrant to dump it all the time, given that it was essentially
needed by developers. Let's make it optional, and disabled by default, only
when "show peers dict" is requested. The default output reminds about the
command. The output has been divided by 5 :

  $ socat - /tmp/sock1  <<< "show peers dict" | wc -l
  125
  $ socat - /tmp/sock1  <<< "show peers" | wc -l
  26

It could be useful to backport this to recent stable versions.